1. Field of the Invention:
The present invention relates to a floating cover, having a gas venting system, for receiving and carrying away gases collecting beneath a floating cover for a liquid storage reservoir.
2. Description of the Prior Art:
Noxious and unpleasant gases are generated by many stored liquids, such as sewage and the like in sewage treatment lagoons or reservoirs. Some facilities of this type are open to the atmosphere and the released gases constitute a nuisance to the surrounding community. Other facilities of this type are provided with rigid covers which completely contain the escaping gass so that collection and removal of the escaping gases is relatively easy. The gases collect below the roof dome and are pumped off for suitable disposition. Floating covers for such facilities are becoming more widely used because they are able to prevent the escape of such gases and yet are considerably less expensive than rigid covers.
By floating cover is meant a cover made of relatively thin, flexible sheet material which lies upon the surface of liquid stored in a reservoir or the like. A cover of this general type wherein provision is made for permitting formation of depending folds in the sheet which serve as collection sumps for rain water and the like is described in U.S. Letters Pat. No. 3,313,443, issued Apr. 11, 1967, and entitled "Floating Cover for a Liquid Storage Reservoir". The edges of such a cover are attached to the reservoir sides or perimeter sufficiently tightly that gases emanating from the reservoir liquid cannot escape but instead collect underneath the cover. Such gases must be carried off or they will cause the cover to inflate or balloon up to an elevation where the cover will be subjected to possible high wind loads, overstressing, and eventual structural failure.
The problem of properly venting floating roof covers is not confined to sewage treatment lagoons, ponds, or reservoirs, but also often exists in other types of reservoirs. For example, the water coming into a fresh water storage reservoir often contains enough dissolved air or other gases that there is continuous gas evolution. In fact, some fresh water storage facilities provide for the bubbling of air through the stored water to aerate it.
In any event, and regardless of the nature of the stored liquid, the disposal of gases from beneath a floating cover is complicated by the fact that the cover rest on top of the liquid and the gases tend to collect in random pockets, frustrating attempts to effect systematic removal. Installation of vents and the like is impractical where the gas collection areas cannot be predetermined.